Demand for cellular telephones and other wireless communications services is continually increasing. As a result, many wireless systems are now configured to operate in more than one frequency band. For example, a cellular system described in U.S. Pat. No. 5,457,734, which issued Oct. 10, 1995 to Eryaman et al. and is entitled "Multi-Band Cellular Radiotelephone System Architecture" is capable of simultaneous operation in two distinct frequency bands centered at 800 MHz and 1.5 GHz. In addition, personal communication services (PCS) wireless systems have recently been configured using a first band centered at 900 MHz and a second band centered at 1.8 GHz. These and other multiple-band wireless communication systems have created a demand for handsets and other types of portable communication terminals that are capable of operating in two or more distinct frequency bands.
In order to minimize the cost and complexity of the front end radio-frequency (RF) circuitry in these multi-band portable terminals, it would be highly desirable to provide a single low-noise amplifier at the front end that can, for example, amplify both the 900 MHz and 1.8 GHz frequency bands. Such an amplifier should have both a low noise figure and a high gain to reduce the effects of noise in subsequent amplifying stages. Unfortunately, conventional low-noise amplifiers are unable to provide acceptable noise and gain performance in multiple wireless bands without unduly increasing the amplifier cost and complexity. For example, application of conventional matching techniques to a low-noise amplifier would generally require that both an input and an output matching network utilize a separate set of at least two or three elements for each of the frequency bands to be matched. A separate set of elements is therefore used to provide a narrowband input or output match for each of the frequency bands. Other conventional approaches may attempt to use a single set of elements to provide a broadband input or output match, but such techniques are very difficult to implement and often unable to meet the performance requirements of multiple frequency bands. As a result of these and other deficiencies of the prior art, it may be necessary for a given handset to include separate amplifiers for each of the frequency bands, or a single, multi-stage amplifier which is both complex and expensive. In either case, the size, cost and power consumption of the handset is unduly increased.
It is therefore apparent that a need exists for a simple and inexpensive low-noise amplifier which can operate in at least two distinct frequency bands, such that the amplifier may be used in a handset or other portable communication terminal of a multi-band wireless system without unduly increasing the size, cost and power consumption of the portable terminal.